(Per)fluoropolyethers (PFPEs) and derivatives thereof are currently used in the lubrication of sliding or moving parts of MRM. In particular, certain PFPE derivatives containing a PFPE chain having terminal and/or non-terminal polar functional groups have shown best performances; indeed, thanks to the high chemical stability of the PFPE chain and to the presence of polar functional groups, such derivatives are able to form an even, thin and long-lasting lubricant film on the surface of the moving parts of MRM. In particular, magnetic disks surfaces are usually coated with a carbon overcoat to which polar functional groups ensure adhesion, thereby preventing the lubricant film from being spun off during revolution of the disk. For example, US 2007060487 (HITACHI GLOBAL STORAGE TECHNOLOGIES) 15 Mar. 2007 discloses lubricants consisting of a PFPE chain with terminal and non-terminal hydroxyl groups.
Among PFPE derivatives suitable for the lubrication of MRM, mention can be made of compounds comprising at least one central phosphazene ring, said ring being substituted with at least one PFPE chain bearing one or more hydroxyl groups. The phosphazene ring is highly stable from the thermal standpoint and further increases the stability of the PFPE chain; without being bound to theory, it is believed that the phosphazene ring acts as a Lewis base which counteracts the catalytic effect on thermal degradation of the PFPE due to the Lewis acids typically present as impurities in the MRM. Examples of such derivatives are disclosed, for example, in US 2002183211 A (AKADA TAMIO ET AL) May 12, 2002, US 2008020171 A (MATSUMURA OIL RES CORP [JP]) Jan. 26, 2006, US 2008305975 (SEAGATE TECHNOLOGY LLC [US]) Nov. 12, 2008, WO 2007/043440 A (MATSUMURA OIL RES CORP [JP]) Apr. 19, 2007, US 2012276417 A (WD MEDIA SINGAPORE PTE LTD) Apr. 19, 2007 and US 2012251843 A (SEAGATE TECHNOLOGY LLC [US]) Oct. 4, 2012.
Among PFPE derivatives disclosed for the lubrication of MRM, mention can also be made of compounds comprising at least one triazine central ring, said ring being substituted with at least one PFPE chain bearing one or more hydroxyl groups. Examples of such derivatives are disclosed, for example, in WO 2012/072532 (SOLVAY SPECIALTY POLYMERS ITALY S.P.A.) Jun. 7, 2012.
HARA, Hiroki, et al. Chemical properties of Fomblin® perfluoropolyether lubricants with arylalkyl groups on hard-disk media. Tribiology Letters. 2001, vol. 11, no. 1, p. 7-13. disclose lubricants for MRM comprising a PFPE chain of formula: —CF2(OCF2CF2)m(OCF2)nOCF2— wherein each end of the chain bears an end moiety selected from those complying of formulae reported below:

This article does not disclose or suggest lubricants bearing hydroxyl groups.
HARA, Hiroki, et al. Chemical properties of a perfluoropolyether lubricant with functional groups of pentafluorobenzyl on hard disk media. Jpn. j. appl. phys. 2001, vol. 40, p. 3349-3353. discloses a perfluoropolyether lubricant (LUB-B) for MRM comprising pentafluorobenzyl functional groups at both ends of the main chain. This article does not disclose or suggest lubricants bearing hydroxyl groups.
KASAI, Paul H., et al. Disk lubricants for spontaneous Adsorption and Grafting to carbon Overcoat by UV Irradiation. Tribol Letter. 2010, no. 38, p. 241-251. disclose both lubricants for MRM comprising a phosphazene ring bearing PFPE chains comprising a hydroxyl group and lubricants comprising a perfluoropolyether chain comprising end moieties complying with formulae:

JP 2009-270093 (MORESCO CORP) discloses a lubricant comprising a compound of formula (1)[HO—(CH2—R2—CH2—O-A-O)n—CH2—R2—CH2—O—CH2]p—R1  (1)
wherein n is from 0 to 6, A is a group represented by —CH2CH(OH)CH2—, R1 is an aromatic group of formula C6H6−p, C6H5−q—O—C6H5−r, and C10H8−p, p is an integer of 3-6, q and r are respectively integers of 0 or more and p+q=r, R2 is —CF2O(CF2CF2O)x(CF2O)yCF2— or —CF2CF2O(CF2CF2CF2O)zCF2CF2—, x and y are respectively real numbers of 0-30 and z is a real number of 1-30. However, this patent application discloses compounds comprising aromatic moieties, wherein chain R2 is bound to said aromatic moiety through a —CH2— group.
In view of the continuing developments in MRM technologies (including heat-assisted magnetic recording techniques, HAMR), the need is still felt for MRM lubricants able to form an even and thin film on the carbon overcoat and also be endowed with high thermo-oxidative stability, coupled with high cohesion with support layers to be lubricated and outstanding lubricating behaviour. It would also be desirable to provide a convenient process for the manufacture of such lubricants on an industrial scale.
EP 2100909 A (SOLVAY SOLEXIS S.P.A) Sep. 16, 2009 discloses compounds suitable, inter alia, as additives for perfluorinated fluids and lubricants. The compounds are addition products of a PFPE peroxide on to a per(halo)fluorinated aromatic compound and comprise at least one perfluorinated non-aromatic cyclic moiety having at least two substituents comprising a PFPE chain and, optionally, conjugated or non-conjugated double bonds. However, the PFPE chain does not bear hydroxyl groups and the use in the lubrication of MRM is not disclosed or suggested.
WO 2012/007374 (SOLVAY SOLEXIS S.P.A.) Jan. 19, 2012 discloses a block copolymer to be used in an elastomer composition; said polymer comprises one or more polyalkylene segments, one or more PFPE segments and at least one per(halo)fluorinated non-aromatic cyclic moiety having chemically bound to at least two sp3 hybridized carbon atoms PFPE chains and having, optionally, conjugated or non-conjugated double bonds. Similarly to EP 2100909, this application neither discloses nor suggests PFPE segments comprising hydroxyl groups and does not refer to the lubrication of MRM.
EP 1354932 A (SOLVAY SOLEXIS SPA) Oct. 22, 2003 discloses stabilizers for PFPE oils at high temperatures comprising a PFPE chain having two chain ends, each chain end bearing a phenyl ring, said being substituted with X and Y groups, including a nitro group. Also this document does not relate to the lubrication of MRM and does not teach or suggest PFPE chains comprising hydroxyl groups.
EP 1659165 A (SOLVAY SOLEXIS S.P.A.) discloses fluorinated additives to be used as stabilizing agents to thermooxidation for fluorinated lubricating oils and greases. Among the others, this patent applications exemplifies a (per)fluoropolyether derivative containing in the chain one pyridine ring substituted with a nitro group and containing at each end group one aromatic ring substituted with two nitro groups. However, the aromatic rings terminate the chains and the (per)fluoropolyether chain does not bear any hydroxy group.
US 2012/0190603 (ASAHI GLASS COMPANY, LIMITED) discloses ether compounds comprising aromatic moieties substituted with one fluorinated ether chain. However, the aromatic rings terminate the chains and the fluorinated ether chain does not bear any hydroxy group.
US 2010/0261039 (HOYA CORPORATION) discloses a magnetic disk comprising a substrate and at least one magnetic layer, a carbon-based protective layer and a lubricating layer that contains a compound that has a perlfuoropolyether main chain in the structure thereof and as an aromatic group at the end of the molecule. However, the aromatic rings are not substituted with an electron-withdrawing group.